Breakaway, or knock down, support structures are used to support objects which must be located near a highway and are subject to occasional impacts by motor vehicles. Breakaway support structures are provided so that when the support structure is impacted by a motor vehicle the support structure will yield to limit damage to a vehicle, the support structure and the object carried by the support structure. Such objects may include mail boxes, signs and lights. Breakaway support structures must be strong enough to withstand low level forces from incidental contact or the wind.
Prior breakaway support structures are not generally designed to be reused following impact. After such structures are impacted the entire member must be replaced.
It is one object of the present invention to provide a support structure for objects having a fracturable link, or shear pin, interconnecting the support structure to a foundation member so that impact by a motor vehicle will cause the fracturable member to break thereby limiting damage to the support member and permitting reuse of the support member. The breakaway support structure also minimizes damage to the motor vehicle by reducing the force applied by the motor vehicle prior to the yielding of the support member.
It is an important object of the present invention to provide an interconnection including at least one shearable member which may be simply replaced after impact without having to reexcavate and anchor the support structure in the ground.
It is another object of the invention to provide two elements in the interconnection between the foundation and the support member which may shear upon impact. According to the present invention, one of the two shearable elements is preferably fracturable from any direction upon application of sufficient lateral force.
Another feature of the present invention is the use of a flexible meaber such as a cable which limits movement of the support structure away from its foundation.
Another aspect of the invention is to provide a breakaway support structure having interengaging portions on the foundation member and support member which align the support member with the foundation member.